power tube question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by jezzzz2003, Jan 24, 2006.


  1. jezzzz2003

    jezzzz2003 Member

    Messages:
    2,794
    Joined:
    Dec 6, 2005
    Location:
    aussie
    Hi...
    I recently emailed our Australian Svetlana distributor asking a few fair questions.
    He ofcourse never returned my email so I thought I would ask you old pros.
    I like using Svetlana winged c 34's
    I have in stock two unmatched pairs.
    One is textered 74, another 76.
    Another unmatched pair is a little further out at 62, the other 68.
    I want to know what these numbers stand for, is it gain, output????
    And furthermore will I notice any difference using them in my 50w?
    Thanks guys.
     
  2. Blue Strat

    Blue Strat Member

    Messages:
    30,007
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    Only your tube supplier knows what HIS numbers mean. Every dealer uses different testers and test methods and there is no uniformity. My guess would be to use the 74 and 76, BIAS the amp/tubes for around 35mA, and start playing. If you have a bias probe (or use any bias method) you'll find out how well matched the tubes are.
     
  3. jbltwin1

    jbltwin1 Member

    Messages:
    267
    Joined:
    Jan 23, 2006
    Location:
    alton, il
    As usual, Mike is right. Those numbers are only good to the guy selling them. They MAY MEAN NOTHING, although they usually do. They are only a guide to what THAT distributor grades his tubes at. Hell, they may be the stock number for all we know. They are a grading of how hot or how much anode to cathode current that THAT PARTICULAR tube uses at THAT PARTICULAR voltage. The only time that is relevant is when you buy replacement tubes from that particular dealer again, you SUPPOSEDLY can just plug and play but I think even that is suicidal. Bias your damned amp folf. Mike.
     
  4. jezzzz2003

    jezzzz2003 Member

    Messages:
    2,794
    Joined:
    Dec 6, 2005
    Location:
    aussie
    Hey hey hey.....
    Dont get narky, I bias my damn amp o.k.
    I wouldnt just plug n play.
    And what does folf mean?
     
  5. donnyjaguar

    donnyjaguar Member

    Messages:
    4,234
    Joined:
    Nov 4, 2005
    Location:
    Canada
    One thing I've learned is that if a supplier offers matched output tubes you'd better buy them. If you just buy in bulk you'll get all the tubes that are all over the map as far as Gm goes. :(
     
  6. VintageJon

    VintageJon Member

    Messages:
    155
    Joined:
    Nov 3, 2005
    Location:
    Austin TX
    The numbers placed on tubes are very confusing but meaningful to the guy that tests them, per Mike.

    Here I mark the cathode current each one pulls in my test rig and the Gm it rates in the Hickok 800. If they are within 10% I call it a match.
    (There are many systems out there and some are more valid than others.)

    Really sorry to hear that your supplier doesn't respond. What are these folks thinking? The wonderful thing about the World Wide Wazoo is that we can respond in near-real-time. This is The-Communication-Age isn't it.

    Mike's guess is a good one and I'd go with that, with the provision that you check them both and see how they spec in your application.

    -Jon
     
  7. jezzzz2003

    jezzzz2003 Member

    Messages:
    2,794
    Joined:
    Dec 6, 2005
    Location:
    aussie
    O.K...

    I called our Aussie distributor this morning after changing power tubes.
    They sound just like they did before except better, I am getting better clarity and they are basically the same match as before so I have not biased.
    I found out his matching process is milliamp to the plate measurement.
    Which im guessing everybodys would be too,
    He explained to me that the 74 and 78 unmatched pair I installed is only 4ma apart
    and will not matter,
    It sounds good to me so I will leave them in unbiased.
    I also want to know what "microphonic" preamp tubes really mean.
    As I noticed at last nights rehearsal that I was getting an unusual amount of early feedback on chords and later on tapped all my preamp tubes to see if they were microphonic..
    One was quite loud when tapping with a screwdriver so I changed it.
    The feedback was still there so I changed all of them to no avail.
    I reintalled the good ones which did not make a tapping sound when tapped with my screwdriver.
    I then changed power tubes and it virtually eliminated the problem.
    Whay are the symptoms of a microphonic tube???
    Thanks guys.
     

Share This Page